Meikuang Anquan (Jul 2024)
Study on gas-liquid-solid multiphase flow laws in CBM reservoir
Abstract
It is of great practical significance to reveal the law of coal powder migration and production in the unsaturated flow stage of the reservoir for the efficient extraction of coalbed methane (CBM). The gas-liquid-solid three-phase flow simulation device was used to set different coal fines particle sizes, injection flow rates, fracture widths and coal fines mass fraction. The experiment of coal fines production and migration characteristics at the initial stage of gas production in coalbed methane reservoirs was carried out, and the variation characteristics of coal fines precipitation, output and gas phase permeability and liquid phase permeability were analyzed. The research results show that with the increase of fracture width, the output quality of coal fines showed an increasing trend, and the depositional volumes of coal fines first increase and then decrease, reaching the maximum value when the fracture width was 0.1 mm. With the increase of coal fines mass fraction, the output values first increase and then decrease (the peak point of 0.15‰), and the depositional volumes of coal fines of different sizes all increase, indicating that the migration of coal fines in the reservoir has a certain extreme value of mass fraction. If it exceeds the extreme value, a large amount of coal fines will deposit and block fractures. Reasonable control of the water and gas production rate of CBM can effectively control the output of coal fines. With the increase of injection flow rate, the amount of pulverized coal deposition and the amount of pulverized coal production increased first and then decreased. When the injection flow rate is 5.0 mL/min, the amount of pulverized coal deposition is maximum, and when the injection flow rate is 7.5 mL/min, the amount of pulverized coal production is relatively high. The evolution characteristics of liquid phase permeability show two trends: gradually decreasing and first stabilizing and then decreasing gradually, while the evolution characteristics of gas permeability are more complex. According to the change of coal permeability, coal fines output and depositional characteristics, coal fines migration in fractures can be divided into three stages: slow deposition, rapid deposition and complete plugging. The research results can provide theoretical guidance for the reasonable control of coal fines production in the field of coalbed methane.
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